This invention relates to the synthesis of alkenoate esters from a corresponding lactone and an alcohol, in the presence of basic catalyst. More specifically, this invention relates to the synthesis of alkyl-4-pentenoate esters from 5-methylbutyrolactone and alcohols.
Alkenoate esters are valuable precursors and monomers in many processes, for example, in nylon intermediates such as caprolactam and adipic acid. For example, methyl-4-pentenoate ester is a precursor for the production of 5-formylvalerates, which can subsequently be converted to caprolactam without producing ammonium sulfate, by hydrogenation and cyclization of aminocaproates. U.S. Pat. No. 5,144,061 discloses a process for preparing alkenoate esters with a terminal double bond starting from a corresponding 5-, 6-, or 7-membered lactone and an alcohol, in presence of an acid catalyst.
U.S. Pat. No. 4,740,613 discloses preparation of 4-pentenoate esters by reaction of gamma-valerolactone with an alcohol in the presence of acidic catalyst at temperatures of 150xc2x0 C. to 400xc2x0 C. The reaction produces an isomeric mixture of 4-pentenoate, 3-pentenoates (cis structure and trans structure), and 2-cis-pentenoate. This reaction is represented by the following equation: 
g-valerolactone alcohol mixture of isomeric pentenoates
wherein, R is an alkyl group of 1 to 6 carbon atoms.
More specifically, the ""613 patent disclosed the reaction of gamma-valerolactone and methanol in the presence of acidic catalysts to give a mixture of methyl pentenoate ester isomers: (1) methyl4-pentenoate ester, (2) cis-methyl-3-pentenoate ester, (3) trans-methyl-3-pentenoate ester and (4) cis-methyl-2-pentenoate ester. This reaction is represented as follows: 
Based on the final composition of all pentenoate esters in the product, the ""613 patent discloses a maximum distribution of the methyl-4-pentenoate ester of 38%. Attempts prior to the ""613 patent reported a maximum distribution of 8% of methyl-4-pentenoate ester (German Laid-Open Application DOS No. 3,412,295 as cited by the ""613 patent). In these prior reactions, methyl-4-pentenoate ester was obtained by isomerization of methyl-3-pentenoate ester (70% trans, 30% cis). The 4-pentenoate product was subsequently isolated from such isomeric mixtures by azeotropic distillation.
However, employing the process conditions of the ""613 patent cannot yield a methyl4-pentenoate ester distribution substantially higher than 38%. Thus, expensive steps for separation of methyl4-pentenoate ester (e.g. distillation) and recycling of the methyl-2- and the methyl-3-pentenoate esters isomers are necessitated. These prior disclosures demonstrate a continuing need for a process for directly producing methyl-4-pentenoate ester as opposed to converting methyl-3-pentenoate ester isomer to methyl-4-pentenoate ester. Consequently, a process which yields a higher selectivity and distribution of 4-pentenoates and a higher conversion of the lactones is desired.
Moreover, although each pentenoate ester isomer can be converted to another isomer, a simple process that produces a particular desired isomer as the major product would be advantageous.
The present invention teaches away from using the acidic catalyst for producing alkenoate esters from lactone and alcohol precursors. The invention teaches a process of using basic catalysts to produce alkenoate esters from lactone and alcohol precursors. Three main objectives are achieved from the process disclosed herein: (1) a higher selectivity of 4-pentenoates than hitherto known; (2) a desired distribution of methyl4-pentenoate; and (3) a higher conversion of the lactone precursor to product. Specifically, the process of the invention provides a selectivity of the methyl-4-pentenoates ester greater than 95%, a distribution of the methyl-4-pentenoate ester isomer in the methyl pentenoate ester product of up to 99% and a corresponding conversion of gamma-valerolactone as high as 70% employing the basic catalyst systems disclosed herein. Moreover, the process of the instant invention provides a direct, one step method of obtaining a higher yield of methyl-4-pentenoate ester.
This invention relates to a process for preparing at least one isomer of alkyl alkenoate ester (III) comprising the steps of contacting lactones of Formula I with an alkanol of Formula II in the presence of a heterogeneous base catalyst to form a mixture containing the corresponding alkyl alkenoate esters, 
wherein: n=0-2; R1, R2, R3, and R4 taken independently are hydrogen, hydrocarbyl or substituted hydrocarbyl, C1-C18 unsubstituted or substituted alkyl, unsubstituted or substituted alkenyl, unsubstituted or substituted cycloalkyl, unsubstituted or substituted cycloalkyl containing at least one heteroatom, unsubstituted or substituted aryl, and unsubstituted or substituted heteroaryl, R5 and R6 taken independently are hydrogen or alkyl with 1 to 5 carbon atoms, wherein the total number of carbons of R5 and R6 do not exceed 5, and R is alkyl with 1 to 6 carbon atoms.
This invention specifically relates to a process for preparing alkyl-4-pentenoate ester isomer in high yields by contacting gamma-valerolactone with alcohol in presence of heterogeneous basic catalyst in the temperature range of from about 250xc2x0 C. to about 500xc2x0 C.